1. Field of the Invention.
A single pilot valve directs pressurized pilot fluid to a downstream spool valve. The spool valve directs the pilot fluid to control a main valve. A pressurized source of supply fluid is connected to the main valve and is selectively directed by the main valve to a downstream apparatus such as a cylinder.
2. Description of Related Art
The present invention, a spool valve, is used in combination with a single pilot valve and a main valve, which selectively directs pressurized supply fluid to a downstream apparatus. This system, the single upstream pilot valve, the spool valve, the main valve and the downstream apparatus are typically located subsea, often at great depths, and are commonly used in the production of oil and natural gas. The present invention, a spool valve, is a normally open two position four way valve. The single upstream pilot valve is typically a solenoid operated normally closed two-way three-position valve. When the pilot valve is closed it isolates the source of pressurized supply fluid and vents downstream pilot fluid, including the pilot fluid in the spool valve to atmosphere.
In the past, spool valves have generally not been used subsea in this type of system. The present invention is an improvement of U.S. Pat. No. 5,901,749 assigned to Gilmore Valve Co., the assignee of the present invention. Prior art subsea systems typically did not include a spool valve. Instead, they utilized two upstream solenoid operated pilot valves to control a main valve, which selectively directed pressurized supply fluid to a downstream apparatus. In prior art subsea systems, one solenoid operated pilot valve was actuated to open the main valve and the second solenoid operated pilot valve was actuated to close the main valve. These subsea solenoid operated pilot valves were connected to a surface control system by a long umbilical. Long umbilicals have to support their own weigh because they run from the surface to the sea floor. These umbilicals contained at least one conduit for pressurized pilot fluid, at least one conduit for pressurized supply fluid, at least one power conductor for each solenoid and at least one control conductor to each solenoid. When the main valve was xe2x80x9conxe2x80x9d it was necessary to keep the solenoid operated pilot valve xe2x80x9conxe2x80x9d which required both electric power and pressurized pilot fluid to be fed to the subsea system. As working depths became greater, it became necessary to reduce the weight of the long umbilical.
One solution was to install a computer subsea with the valves. This reduced the weight of the umbilical because the control conductor ran from the computer to each solenoid operated pilot valve rather than to the surface. In this improved umbilical design, a signal conductor ran from the computer to the surface to carry data along with a single power conductor and the pilot fluid conductor. This improved umbilical eliminated the control conductors running from the surface to each solenoid. The signal conductor sent data from the surface to the subsea computer which then switched power on or off to each solenoid valve. Although the weight of the umbilical has been reduced, the solenoid operated pilot valves still had electrical power requirements because they had to remain in the xe2x80x9conxe2x80x9d position to keep the main valve open.
The present invention uses only a single upstream pilot valve rather than two. Clearly, the elimination of the second solenoid operated pilot valve and the wiring used to connect it to a subsea computer is an advantage.
The present invention has another advantage over the prior art because this spool valve does not have to remain in the xe2x80x9conxe2x80x9d position to keep the mail valve open. In other words, the present spool valve does not require continuous application of pressurized pilot fluid to hold its position. Instead, the present spool valve typically needs to be activated for several seconds. This pulse operation reduces the electrical power requirements to the solenoid operated pilot valve. Reduced power requirements of the pilot means that the power conductor in the umbilical can be reduced in size to lighten the umbilical even further.
The spool valve of the present invention can be produced as an integrated design with the main valve, all in a single body or the spool valve and main valve can be produced separately with two distinct bodies. When the spool valve of the present invention is combined with a latching main valve, one has the capacity of having the main valve turned to the xe2x80x9coffxe2x80x9d position if the source of pressurized supply fluid should fail. This combination leads to benefits greatly appreciated by system designers attempting to control multiple functions at great subsea depths including lighter, less costly umbilical connections and smaller, lighter, packages.
The spool valve is connected to a single upstream pilot valve and a main valve to open and close the main valve in response to fluid signals from the pilot valve. The pilot valve is connected to a source of pressurized supply fluid, typically at pressures of between 1,000-3,000 psi, which is selectively directed to an open chamber to open the main valve or to a close chamber to close the main valve. The main valve is connected to a source of pressurized supply fluid, which is selectively directed to a downstream apparatus such as a cylinder. The supply fluid is pressurized at about 10,000 psi. The upstream pilot valve, the spool valve and the main valve are all vented to atmosphere. In subsea applications, atmosphere means the surrounding seawater. To be environmentally friendly, the pilot fluid and the supply fluid are typically fresh water. The spool valve and the main valve can be manufactured as an integrated unit having a single body. In an alternative embodiment, the spool valve can be manufactured separate from the main valve, each of which has a separate body.